Add support for PL172 memory-controller

This patch set adds a memory driver and documentation for the ARM PL172. This driver makes it possible to configure the static memory chip selects on the ARM PL172 MultiPort Memory Controller from a set of properties in DT. Configuration of dynamic memory (SDRAM) is not supported and is left to the boot loader. The intended usage is to setup timing and configuration for static memory devices like NAND and NOR Flash before they are probed by a driver. Pretty much what like all the other memory drivers do.

As drivers/memory doesn't seem to have a maintainer of it's own I hope this patch set can go through the armsoc-drivers branch.

The previous version of the patch set didn't recive recivce much feedback and the cover letter can be found here:
http://marc.info/?l=devicetree&m=143024189625522&w=2

DT bindings for PL172 is based on the bindings for the TI AEMIF memory controller. PL172 can be found on a number of NXP devices like the LPC18xx family.

Tested on Embedded Artists' LPC4357 Developer's Kit with NOR Flash (SST39VF320) and 74LCV16374 (gpio-74x164) on MPMC.

Changes since v1:
- Add proper commit messages
- Misc clean ups

Joachim Eastwood (2):
memory: add ARM PL172 MultiPort Memory Controller driver
doc: dt: add documentation for pl172 memory bindings